Agonists of liver X receptors (LXR) α and β are important regulators of cholesterol metabolism but agonism of the LXRα subtype appears to cause hepatic lipogenesis suggesting LXRβ-selective activators are attractive new lipid lowering drugs. interest in therapeutically targeting reverse cholesterol transport (RCT) the process of cholesterol delivery from peripheral cells to the liver for subsequent elimination.4?6 The liver X receptors (LXRα and LXRβ) belong to the nuclear receptor superfamily and are key regulators of cholesterol GS-9137 homeostasis and RCT.7?9 LXRα is highly expressed in metabolically active tissues such as liver intestine adipose tissue and macrophages whereas LXRβ is ubiquitously expressed. Both subtypes share 77 sequence homology in their DNA binding and ligand binding domain. Activated by endogenous oxysterol ligands as well as by several synthetic ligands 10 LXRs increase reverse cholesterol efflux from cells including macrophages of atherosclerotic lesion sites via ATP-binding cassette transporters A1 and G1 (ABCA1 and ABCG1). Extracellular cholesterol is transported to the liver by cholesterol acceptors such as HDL and lipid-poor apolipoproteins and converted to bile acids for secretion into bile and its elimination into feces. In addition to the receptors regulatory role in cholesterol metabolism LXRs also possess anti-inflammatory properties.11 12 The antiatherosclerotic effect of LXR activation has been demonstrated in numerous studies of murine atherosclerosis models. Treatment of atherosclerotic mice with an LXR agonist reduces disease development while the loss of LXR expression results in accelerated atherosclerosis.10 13 14 Despite the antiatherosclerotic properties of LXR agonists their use as therapeutic agents has been hampered by unfavorable side effects of LXR stimulation such as increased hepatic lipogenesis hypertriglyceridemia and liver steatosis.15 16 GS-9137 These adverse effects Rabbit Polyclonal to ALX3. are attributed to LXRα which is the predominant LXR subtype in the liver inducing the expression of genes involved in fatty acid and triglyceride synthesis.17 18 Hence it has been proposed that specific targeting of LXRβ may retain antiatherosclerotic benefits while avoiding hepatic lipogenesis and the development of steatosis. However given the degree of structural similarity of the two LXR isoforms combined with the high flexibility of the binding pocket subtype-selective agonists may be difficult to attain. Nevertheless Molteni et al. recently discovered a series of N-acylthiadiazolines subtrates with selectivity for LXRβ.19 The aim of this study was to apply a virtual screening workflow to retrieve LXRβ-selective compounds from a 3D compound database. In vitro evaluation of these compounds employing a cell-based LXRα/β-selective luciferase assay GS-9137 should reveal novel LXR ligands with the desired selectivity. In a previously published GS-9137 study a set of six structure-based pharmacophore models for LXR agonists was developed.20 The models were experimentally validated by biological confirmation of the activity of 18 synthetic LXR agonists they had predicted. Four of these virtual hits were active in an assay that determined the relative induction of the LXR-driven luciferase reporter gene ABCA1 but they were not tested on subtype specificity. To determine whether the available six models had the ability to find the LXRβ-selective scaffold proposed by Molteni et al. 19 a testset of 14 compounds was assembled and sorted by LXR subtype selectivity (Supporting Information). From these 14 compounds a 3D multiconformational library was calculated in Discovery Studio21 using BEST (flexible) settings and a maximum of 100 conformers per molecule. This library was screened against the six pharmacophore models using BEST settings which allow for a modest conformational ligand change during the screening optimizing its fitting into the model. Two models were not able to find any compounds from the data set and were discarded. One model found just one moderately selective structure and was also discarded. The three models 1pqc 1 and 3 (Figure ?(Figure1)1) found a significant number of highly selective compounds and were therefore selected for the prospective virtual screening for novel LXRβ-selective ligands. Detailed results on these virtual screening experiments and hit lists are available in the Supporting Information. Figure 1 Pharmacophore models that showed a significant.